In recent years, with a start of the digitization of television broadcasting, an information recording medium that is able to store or record mass digital data is demanded. For example, one of the basic methods to promote high density recording and reproducing in the field of optical disks is to make as small as possible the diameter of a spot of a light focused by the optical disk for recording and reproducing information.
In the following, an optical disk will be described as being a typical example, but the disk for use in the recording and reproducing device according to the invention is not limited to an optical disk. Any of disk-shaped recording media, such as a phase change memory, a magneto-optic memory, and a hologram memory, is applicable.
When a laser beam is focused to perform a high-density recording or reproducing on an optical disk, it is important to make axial runout of the disk surface at the time of the disk rotation, i.e., surface vibration, as small as possible.
Improvement in the speed of the data transfer rate is demanded with increasing amount of information to be recorded in an optical disk. For example, a target data transfer rate for the recording of HDTV image for broadcasting is 250 Mbps or more. When this data transfer rate is used for the recording on the whole recording surface of an optical disk, the rotation of the disk at a high speed above 15000 rpm is needed in order to secure the data transfer rate in the inside peripheral portion of the disk.
Even in the case of such a high speed rotation, it is necessary to make small the surface vibration of the disk with the successive high-speed rotation in order to ensure the stability of the focus servo to the disk at the time of recording and reproducing.
Conventionally, a method of holding a disk of a rigid body on a turntable with elastic bodies is known as a countermeasure for preventing the surface vibration due to vibrations of the disk. For example, each of Japanese Laid-Open Patent Application No. 6-28752, Japanese Patent No. 2882379 and Japanese Laid-Open Patent Application No. 5-54502 discloses a device for preventing vibrations of a disk.
In these vibration preventing devices according to the related art, the hard disk that is usually made of a rigid material is fixed to a turntable (spindle) via an elastic material. Using the elastic material, the vibration (resonance) of the hard disk when it is rotated is prevented, and the possible vibration caused by the poor connection of the disk holding part by the inclusion of dirt therein is prevented.
However, the vibration preventing devices according to the related art are unsuitable for recording and reproducing of the hard disk made of a rigid material when it is rotated at a high speed over 10000 rpm.
A flexible disk that is suitable for the high speed rotation is known. And a method using an aerodynamic stabilization unit when a flexible disk is rotated at a high speed is known. This method is proposed as a surface deflection preventing measure for high speed rotation of a flexible disk.
When the flexible disk is rotated at a high speed, surface vibration like a waving phenomenon are easily developed with the high-speed rotation of the flexible disk, where the phenomenon is different from the surface vibration due to the resonance as in the disk of a rigid material.
To prevent such surface vibration of a flexible disk, the method using the aerodynamic stabilization unit is usable. For example, each of Japanese Laid-Open Patent Application No. 2006-107699, Japanese Laid-Open Patent Application No. 2007-149311 and Japanese Laid-Open Patent Application No. 2006-344291 discloses a stabilizer member (or stabilizer). In the recording and reproducing device disclosed in these publications, the configuration of the stabilizer arranged on the surface of a flexible disk is modified. Thereby, the rotating disk is stabilized using the aerodynamic action between the disk and the stabilizer with the modified configuration, and recording and reproducing of information to the stabilized disk becomes possible.
Specifically, in the recording and reproducing device disclosed in Japanese Laid-Open Patent Application No. 2006-107699 or No. 2007-149311, a plane-surface stabilizer is arranged to face a flexible disk, or a curved concave surface stabilizer is arranged to face a flexible disk. A gap between the stabilizer and the disk surface is set to 0.05-0.30 mm, and the surface vibration of the disk when the disk is rotated at a high speed over 10000 rpm can be suppressed.
In the recording and reproducing device disclosed in Japanese Laid-Open Patent Application No. 2006-344291, a spacer with an arbitrary thickness is disposed between a flexible disk and a stabilizer plate, and the vibration of the disk is suppressed by using the flow of the incoming air from an air introducing hole in the inside peripheral portion of the spacer.
When these methods according to the related art are used, the vibration of the flexible disk is prevented by the stabilizer. In the cases of the existing recording media made of a rigid body, such as CD, DVD, BD, and HD-DVD, it is difficult to use the rotational speed over 10000 rpm. However, when these methods according to the related art are used, there is the possibility that enables stable driving at the rotational speed over 10000 rpm. Specifically, Japanese Laid-Open Patent Application No. 2006-107699 or No. 2007-149311 describes that a possible highest rotational speed of over 12000 rpm is usable for the rotation of a flexible disk.
For the time being, there is no actual recording and reproducing system which is capable of rotating a flexible disk at a high speed over 10000 rpm to perform recording and reproducing, and the practical solution is not yet known. Taking into consideration a disk rotating device according to the related art as shown in FIG. 18, the feasibility of a flexible disk 1 when it is rotated by the disk rotating device at a high speed over 10000 rpm has been tested.
As shown in FIG. 18, the flexible disk 1 is disposed between a damper 6 and a turntable 5 connected to a spindle 3, and the disk 1 is fixed there. When the disk 1 in this condition is rotated at a high speed over 10000 rpm, the problem that the disk 1 held on the turntable 5 is added a distortion in the vicinity of the inside peripheral portion. This distortion is accumulated and increased by the repetition of increasing and decreasing of the disk rotational speed and/or by the repetition of approaching or separating of the stabilizer 30 (in which the stabilizer 30 is moved in one of the approaching and separating directions according to the changes of the disk rotational speed).
The accumulated distortion may cause contacting or sliding of the disk 1 and the stabilizer 30 in the region of low rotational speeds. If the contacting or sliding of the disk 1 and the stabilizer 30 takes place, large surface vibration of the disk will be developed and the quality of the recording and reproducing signal from the recording head will be significantly degraded. If the operation of starting and stopping the rotation is repeated further, the disk 1 contacts the stabilizer 30, which may cause a fatal error and the rotation of the disk 1 may be stopped.
The arrangement of elastic bodies between the turntable and the disk, as disclosed in Japanese Laid-Open Patent Application No. 6-28752 or Japanese Patent No. 2882379, is tested for determining whether the arrangement prevents the problem or not. However, even if only one surface of the disk is fixed with the elastic material as disclosed in Japanese Laid-Open Patent Application No. 6-28752 or Japanese Patent No. 2882379, it is difficult to reduce efficiently the distortion of the disk in the drive operation including high speed rotation over 10000 rpm.
Even if both surfaces of the disk are fixed with elastic bodies as disclosed in Japanese Laid-Open Patent Application No. 5-54502, the contact surface of the elastic body and the disk is formed into a thin-line circular ring. A small amount of shifting the contact positions of the disk and the elastic body on the front and back surfaces will enlarge the distortion of the disk remarkably.
Thus, even if the composition for preventing the resonance of the rotating hard disk of a rigid material is applied to the disk rotating device for rotating the flexible disk, it is impossible to prevent the distortion of the inside peripheral portion of the flexible disk caused by the repetition of increasing and decreasing of the disk rotational speed and/or by the repetition of approaching or separating of the stabilizer 30.